/Engine/Plugins/FX/Niagara/Source/Niagara/Public/NiagaraComponent.h
Sets the fixed bounds for the system instance, this overrides all other bounds. The box is expected to be in local space not world space. A default uninitialized box will clear the fixed bounds and revert back to system fixed / dynamic bounds.
[UFUNCTION](Programming/UnrealArchitecture/Reference/Functions)(BlueprintCallable, Category=Niagara) void SetSystemFixedBounds ( FBox LocalBounds )